The aim of a phase I monotherapy study in HIV-infected volunteers is to define and select a dose and schedule according to pharmacokinetics/ dynamics and tolerability. FTC is a nucleoside analogue that structurally resembles 3TC, but has 10-fold greater (in vitro) potency. In patients receiving 3TC alone, a fully resistant viral population develops within 12 weeks. Patients for this study must be 3TC naive.